Two live attenuated PIV3 candidate vaccines are in Phase 1-2 trials in human infants and children, namely the cold-passaged 45 mutant of the JS wildtype human PIV3 and the antigenically related bovine PIV3. A complete cDNA copy of the JS strain of human PIV3 has been constructed. This cDNA has the exact coding sequence of the wild type virus except for engineered mutations that will permit the transfectant virus to escape neutralization by monoclonal antibodies that neutralize the infectivity of the helper virus. With this cDNA, it is now possible in the coming year to attempt to rescue infectious virus from RNA generated from this cDNA.